A series of failures in Research In Motion's private network disrupted BlackBerry service to millions of customers across four continents.

Extensive delays hit Europe, the Middle East, Africa and India on Monday and the problems spread to Brazil, Chile and Argentina on Tuesday.

"The messaging and browsing delays being experienced ... were caused by a core switch failure within RIM's infrastructure," the company said in a emailed update late on Tuesday afternoon in Toronto.

RIM's BlackBerry service has long been prized by executives and politicians who rely on its security and reliability to deliver email and other messaging to mobile workers.

The Canadian company manages this service via servers parked within enterprises and hooked up to a proprietary network carried by wireless operators.

"Although the system is designed to failover to a back-up switch, the failover did not function as previously tested," RIM said.

Failover refers to the automatic switching of service to a standby server in the case of a failure of a main system.

RIM hosts a number of network operating centres, including one at its headquarters in Waterloo, Ontario, and another in southern England, which manage the massive amounts of data that flow through its system.

RIM said it was now working to clear a large backlog of data and restore service as quickly as possible.

"We apologize for any inconvenience and we will continue to keep you informed," it said.

RIM had earlier said it had resolved problems disrupting its services in Europe, the Middle East and Africa (EMEA).

The outages are just another headache for RIM, which is losing ground in the corporate email market it once took for granted as employees increasingly push to use their personal devices, typically Apple's iPhones and iPads, and to a lesser extent devices using Google's Android software, in the workplace.

It is also facing calls from some investors for a break-up, sale or change of management following recent dismal results and a lackluster reception of its PlayBook tablet computer, designed to challenge Apple's iPad.

"The current situation with the BlackBerry outages couldn't come at a worse time for RIM, following some harsh criticism in recent months," Informa Telecoms & Media analyst Malik Saadi said in a statement.

"Some businesses may see this as a good reason to re-evaluate their reliance on centralized servers and instead look to investing in more corporately controlled servers.

"Not only would this enable IT departments to minimize the risk of unforeseen collapses, but it could also give employees more flexibility to use their own devices."

Network operators and users in EMEA tweeted that email and BlackBerry Messenger services were not working from around 1100 GMT. Network operator T-Mobile said on its website that the problems were due to a European-wide outage on the BlackBerry network.

It said: "RIM has apologized for the interruption to services and said it's working to restore normal operations."

Earlier, RIM said it had restored BlackBerry services in the region, some 20 hours after users in EMEA and India first reported problems with email and BlackBerry Messenger.

In its latest update, RIM did not say when it expected the outage to be fully resolved.